Sound screen



June 29 1926. 1,590,689

' I F. L. HOPWOOD S OUND S GREEN Filed July '7, 1920 2 Sheets-$heet l June 29 1926.

F. L. HOPWOOD SOUND SCREEN I Filed July 7, 1920 2 Sheets-Sheet 2 I ///E//f//////////////// W/g/T 52W #0 3 aye/ 4 2 14% m Patented June 29, 1926.

UNITED STATES PATENT OFFHO.

FRANK LLOYD HOPWOOD, OF LONDON. ENGLAND, ASSIGNOR TO SUBMARINE SIGNAL COMPANY, OF PORTLAND, MAINE, A CORPORATION OF MAINE.

SOUND SCREEN.

Application filed July 7, 1920,

Serial N'o. 394,542, and in Great Britain December 11, 1918.

(GRANTED UNDER THE PROVISIONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L, 1313.)

This invention relates to underwater sound detecting apparatus of the single or double diaphragm directional hydrophone t'v e.

.lhc baflies or sound screen as hitherto used for directional purposes possess a disadvantage in that they are not capable of adjustment but when completed each bafiie has to be used at a determined and invariable distance fromthe diaphragm of the hydrophone. easy to construct a battle which will be operative at a distance exceeding say two inches from the hydrophone diaphragm it is difficult to make a number of such battles which will work interchangeably or at a less distance. Further, out of those bullies which prove defective the majority are so because they destroy the bi-directional qualities of a hydrophone before they endow it with unidirectional qualities According to this invention the battle coniprises a plate-like member in which is a closed chamber containing a measured and variable quantity of liquid which does not completely fill the chamber. 'In addition to the liquid the chamber may contain a number of small loose bodies formed of suitable material and of similar size and shape such as lead shot. The chamber is shallow and of its two main walls one is relatively thin while the other may be thin or rela-' tively thick. One or more openings are formed through the thicker wall into the chamber and means are provided for closing and sealing these openings as for example by means of screw plugs. The liquid used is preferably oil or water (either fresh or salt) and the desired quantity is inserted into the chamber through one of the openings a second opening serving for the escape of air. When the liquid has been inserted the openings are closed and sealed. That portion of the chamber which is not occupied by the liquid or by the loose bodies may contain air or gas or air may be exhausted therefrom.

A baflle thus constructed can be adjusted by varying the quantity of liquid within the chamber so that the baflle will operate over a comparatively wide range of distances from the hydrophone diaphragm. Further, a baffle which may be defective in the manner above indicated may in some cases be rendered efiicient by modifying it in aclVhile itis comparatively oordance with the present invention. The result of inserting liquid in the chamber is to diminish the distance between the baflle and the hydrophone at which the best working is obtained and'to tend to correct what may be termed overeffectiveness.

The invention may be put into practice in yarious ways but the accompanying drawmgs illustrate by way of example a convenient construction that maybe adopted.

In these drawings Figure 1 is an. elevation of the improved bafile.

Figure 2 is a section on the line 2-2 of Figure 1.

Fig. 3 shows an arrangement in elevation whereby my invention may be put into practice, and 4 Fig. 4 is a sectional view showing details of the lower end of Fig. 3.

A plate A of suitable diameter and thickness constructed of xylonite or other similar non-resonant material has a circular recess B formed in it and of such depth that the thickness of the 'plate A which forms one wall of the recess is reduced considerably so as to constitute a relatively thin wall for the closed chamber. A .xylonite disc C of substantial thickness is provided with a flange C round its periphery and adjacent to the flange a part C of reduced diameter which is screw-threaded to engage the correspondingly screw-threaded cylindrical wall of the recess B in the bafile plate A. A washer D of suitable. material such as that known under the registered trade mark Dexine is disposed beneath the flange C of the disc C and the face of the baflle plate A around the recess B and the disc C is then screwed home. relatively thick wall for the chamber B which is thus formed within the bafile plate A between thedisc C and the opposite and relatively thin wall A of the recess. In this shallow circular chamber B are as many lead shot E as the chamber wi l contain the shot being similar in size and the diameter of each shot being slightly less than the distance between the two opposite flat walls of the chamber. are formed through the thick wall of the disc C each hole being screw-threaded and provided with a screw plug F which serves to close and seal the hole. Before these plugs are inserted'a measured quantity of The disc C constitutes a laced Two holes C .liquid G for example water is poured into the chamber B the quantity being insufficient to completely fill the cavity. The

amount of water employed ma vary in accordance with requirements ut as mentioned in nocase must be the whole of the chamber be filled. When the liquid has been placed in the chamber the plugs F are inserted in the holes and the chamber iscompletely sealed up. In place of emplo ing movable plugs the openings into t e chamber may be permanently closed and sealed after the liquid has been inserted.

Though, as above described, the baflle is formed of xylonite it may be constructed of other'suitable material for example ebonite,

' lead, glass, brass or other suitable m'etaL The disc 3C which constitutes the thicker wall of the chamber and serves toclose in the one side of the recess B in the main plate A may be fixed in place otherwise than by screwing. Forexample this disc when formed of celluloid ma be cemented in place. In place of water 011 may be used or a viscous substance such as rubber solution.

' With a baflie having a chamber of such dimensions as will'contain 250 lead shot each of 1 3' of an inch diameter it has been inc found that the best working {distance is about 2 4 of an inch from the hydrophone diaphragm. When three cubic centimetres of water was placed in the chamber of this dia hragm this distance was reduced to 1 fies. If more water be added the distance will be still further reduced but if an excess of wateris placed in the chamber the baflle may be rendered inoperative. If no shotare used a greater quantity of liquid is necessary in order to make the baflie workv at I a given distance from the hydrophone.

In Fig. 3 the baflle is shown at 1 arranged in relation to a microphone casing 2 which is sup orted at the lower end of a tube 3 throng which arecarried the microphone construction. The bafile late A is provided with holes 9 through w ich' pass bolts 10 whichare screwed into the casing 6, the parts being held in proper relation by nuts 11, 12 being a ring preferably of brass for protecting the balfle from accidental injury. A What I claim as my invention and desire to secure b Letters Patent is 1. A ba e for use with underwater sound detecting means comprising a plate-like body having a tightly closed chamber containing a quantity of liquid, there being space in said chamber unfilled by said liquid. I

2. A bafile for use with underwater sound detecting means comprising a plate-like body having a tightl closed chambercontaining a plurality 0 small loose bodies of solid material and which are of similar size and shape, said chamber also containing a quantity of liquid, therebeing space in said chamber unfilled by said liquid and said loose bodies.

3; A balfie for use with underwater sound detecting means, comprising a plate havin a recess therein, and a disk member locate to close said recess to form a chamber in said balile, said chamber having therein a pllurality of loose bodies of similar size and s a e. 1

43A baflle for use with underwater sound detecting means, comprising a plate having a recess therein, and a disk member located to close said recess to form a chamber in said baflie, said chamber having therein a plurality of loose bodies of similar size and shape and being partially filled with a liquid.

5. A bafille for use with underwater sound detecting means, comprising a plate havin a recess therein, and a disk member locate to close said recess to form a chamber in said baflie, one of the opposing walls of said chamberbeing relatively thincompared with the other.

6. A bafile for use with underwater sound detecting means, comprising a. plate-like body having a chamber therein, said chain- -ber being partially filled with liquid, and said plate-like body having means whereby said chamber may be filled with liquid and said liquid may be hermetically sealed therem name to this specification; Y

FRANK LLOYD HOPWOOD.

In .testinionywhereof I have signed 

